Saliva
Chemical Composition:
- Water: 99% of saliva, serving as a solvent.
- Electrolytes: Sodium, potassium, calcium, bicarbonate, and phosphate.
- Mucins: Glycoproteins that lubricate food and form a protective mucus layer.
Enzymes:
- Amylase (Ptyalin): Begins the breakdown of starch into maltose.
- Lingual Lipase: Initiates the digestion of lipids, particularly in infants.
Other Components: Lysozyme (antibacterial), immunoglobulin A (immune protection), and various growth factors.
Gastric Fluid
Chemical Composition:
- Hydrochloric Acid (HCl): Lowers pH to 1-2, denatures proteins, activates pepsinogen to pepsin, and kills microbes.
- Pepsinogen: An inactive precursor that is converted to pepsin, a protease, in the acidic environment.
- Intrinsic Factor: Glycoprotein essential for the absorption of vitamin B12.
- Mucus: Protects the stomach lining from acidic environment and digestive enzymes.
Enzymes:
- Pepsin: Breaks down proteins into smaller peptides.
- Gastric Lipase: Contributes to the digestion of lipids.
Pancreatic Fluid
Chemical Composition:
Water: Majority of the fluid.
- Electrolytes: Bicarbonate ions neutralize stomach acid in the small intestine.
Enzymes:
- Proteases:
- Trypsinogen: Converted to trypsin in the small intestine, which then activates other proteases.
- Chymotrypsinogen: Converted to chymotrypsin, further breaking down proteins.
- Procarboxypeptidase: Activated to carboxypeptidase, cleaves amino acids from the carboxyl end of proteins.
- Amylase: Continues the breakdown of carbohydrates.
- Lipase: Breaks down triglycerides into free fatty acids and monoglycerides.
- Nucleases: Degrade nucleic acids (DNA and RNA) into nucleotides.